Sulfur-containing polyurethane base lens resin

ABSTRACT

A sulfur-containing polyurethane base lens resin is obtained by reacting one or more isocyanate compounds, which have two or more NCO groups, with one or more OH-containing compounds, which have two or more OH groups, in such proportions that the molar ratio of NCO groups to OH groups ranges from 0.5 to 1.5. At least one of said one or more OH-containing compounds contains one or more sulfur atoms in the molecule thereof. The total content of sulfur atoms in all OH-containing compounds is 20 wt. % or higher.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to a sulfur(S-containing polyurethane base lensresin having a high refractive index and good machinability such as highdegrees of easiness in its cutting and polishing (hereinafter called"cutting and polishing easiness" for the sake of brevity).

(2) Description of the Prior Art

In Japan, more and more plastic lenses have recently been employed aseyeglass lenses and camera lenses and in optical devices, since they arelighter and less fragile compared with inorganic glass lenses and permitcoloration. As a representative resin employed widely for the abovepurposes these days, may be mentioned a radical polymerization productof diethylene glycol bisallyl carbonate. The radical polymerizationproduct will hereinafter be abbreviated as "DAC resin". Although the DACresin has various advantages such as excellent impact resistance,reduced temperature dependency of lenses' refractive powers, lightweight, superb colorability, good machinability such as good cutting andpolishing easiness, etc., it cannot be considered to have sufficientproperties as a resin for lenses in view of the recent trend towardfashion-oriented lenses in the field of eyeglass lenses.

As the most serious drawback of the DAC resin, its refractive index issmaller compared with those of inorganic lenses (refractive index of atypical inorganic lens, N_(D) ²⁰° C. : 1.52; refractive index of a DACresin lens N_(D) ²⁰° C. : 1.50). When the DAC resin is molded into alens, the lens has a greater thickness. In the case of highrefractive-power eyeglass lenses for the near-sighted in particular, thelenses have great peripheral thicknesses. Use of the DAC resin cannotachieve weight reduction and moreover results in eyeglass lens of poorvisual attraction. Accordingly, lenses which make use of the DAC resinas a raw material are pronely shunned due to the recent tendency toplace importance on fashionability.

For the reasons mentioned above, there is an outstanding demand for alens resin having a higher refractive index than the DAC resin, in otherwords, capable of providing thinner lens thicknesses than the DAC resin.

Certain urethane base resins have been known as typical lens resinscapable of achieving high refractive indexes. For example, there hasbeen known a urethane resin obtained by a reaction of an isocyanatecompound with a hydroxyl-containing compound such as diethylene glycol(Japanese Patent Laid-Open No. 136601/1982 or 136602/1982) or with ahalogen- and hydroxyl-containing compound such as tetrabromobisphenol A(Japanese Patent Laid-Open No. 164615/1983).

These urethane-base resins are however unable to obtain refractiveindexes beyond a certain level. In order to obtain a resin having arefractive index, N_(D) ²⁰° C., in the neighborhood of about 1.60 orhigher, it is indispensable to use an aromatic isocyanate and/or amonomer containing many halogen atoms as substituents therein. However,use of such monomers leads to a drawback in external appearance that theresultant resin is colored and another drawback in chemical and physicalproperties that the resultant resin has poor weatherability and poorcutting and polishing easiness.

SUMMARY OF THE INVENTION

The principal object of this invention is to provide a lens resin whichhas a refractive index substantially equal to or higher than than theabove-described urethane-base resins, is free of defects in externalappearance such as coloration and enjoys excellent weatherability andgood machinability such as good cutting and polishing easiness.

The present inventors have carried out an extensive investigation with aview toward attaining the above object of this invention, leading tocompletion of this invention.

In one aspect of this invention, there is thus provided asulfur-containing polyurethane base lens resin obtained by reacting oneor more isocyanate compounds, which have two or more NCO groups, withone or more OH-containing compounds, which have two or more OH groups,in such proportions that the ratio of NCO groups to OH groups rangesfrom 0.5 to 1.5. At least one of said one or more OH-containingcompounds contains one or more sulfur atoms in the molecule. The totalcontent of sulfur atoms in all OH-containing compounds is 20 wt. % orhigher.

When the sulfur-containing polyurethane base lens of this invention isused, a lens having a very high refractive index can be obtained.Indeed, in case kinds of an isocyanate compound and an OH-containingcompound are fitly selected, a refractive index (N_(D) ²⁰° C.) as highas 1.60 or even higher can easily be obtained. In addition, it is freeof defects in external appearance such as coloration and also excellentin weatherability. Further, the above-described conventionalurethane-base resins showed poor machinability such as poor cutting andpolishing easiness unless a trifunctional or higher compound wasincorporated. The resin of this invention has good machinability such asgood cutting and polishing easiness, which is required for lens resins,without absolute need for incorporation of any trifunctionalthree-dimensionally crosslinking agent.

The above and other objects, features and advantages of this inventionwill become apparent from the following description and the appendedclaims.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

In the present invention, one or more isocyanate compounds can be usedas one of the two types of starting raw materials. However, a majorfraction of the starting isocyanate raw material may preferably becomposed of a diisocyanate. The one or more isocyanate compounds may beeither aromatic or aliphatic. Aromatic isocyanate compounds may benucleus-substituted by one or more halogens and/or the like. As theseisocyanate compounds, may, for example, be mentioned m-xylylenediisocyanate, p-xylylene diisocyanate, tetrachloro-m-xylylenediisocyanate, tetrachloro-p-xylylene diisocyanate, hexamethylenediisocyanate, isophorone diisocyanate, tolylene diisocyanate,4,4'-diphenylmethane diisocyanate, the biuret reaction product ofhexamethylene diisocyanate, the adduct reaction product of hexamethylenediisocyanate and trimethylolpropane, 4,4'-dichlorohexylmethanediisocyanate and 2-isocyanatoethyl 2,6-diisocyanatohexanoate. Amongthese isocyanate compounds, particularly-preferable isocyanate compoundsare aromatic diisocyanates, in each of which two side-chain alkyl groupshave been substituted by two NCO groups, such as m-xylylenediisocyanate, and aliphatic diisocyanates such as hexamethylenediisocyanate.

On the other hand, one or more OH-containing compounds, each of whichcontains one or more sulfur atoms in its molecule, can be used as theother starting raw material. However, a major fraction of the startingOH-containing raw material must be composed of a compound containing twoor more OH groups. As these compounds each of which contains one or moresulfur atoms in its molecule, may, for example, be mentioneddi(2-hydroxyethyl) sulfide, 1,2-bis-(2-hydroxyethylmercapto)ethane,bis-(2-hydroxyethyl)-disulfide, 1,4-dithian-2,5-diol and so on.

In the present invention, one or more of these OH-containing compoundseach of which contains one or more sulfur atoms in its molecule may beused either by themselves or in combination with an OH-containingcompound which does not contain any sulfur atom. Regardless of the typeof each OH-containing compound employed, the desired resin which thepresent invention intends to provide cannot be obtained unless one ormore OH-containing compounds containing at least 20 wt. % or preferably25-40 wt. % of sulfur atoms in total in their molecules are used upontheir reactions with the one or more isocyanate compounds.

It is necessary to use these OH-containing compounds, each of whichcontains one or more sulfur atoms, and the above-mentioned isocyanatecompounds in such proportions that the NCO/OH ratio falls within a rangeof 0.5-1.5. Outside this range, the resultant resin may not be hardenedto any sufficient extent or various other properties as a lens resin,which the present invention intends to provide, may be reduced.

In order to obtain high-hardness lenses within the above group ratiorange, it is preferable as the isocyanate and the OH-containing startingraw materials, in addition to those having two functional (NCO or OH)groups, to suitably add an isocyanate compound containing three or moreNCO groups and/or a polyol such as trimethylolpropane or pentaerythritolas three-dimensionally crosslinking agents.

Besides, it is also feasible, without causing any problems orinconvenience, to add a radical-polymerizable raw material such asdiethylene glycol bis(allyl carbonate) (DAC), an acrylic ester, amethacrylic ester or a styrene derivative along with its radicalpolymerization initiator, an ultraviolet absorbent and/or antioxidantfor improving the light resistance, etc. in small amounts depending whatrequirements would be imposed as a lens resin, so long as theseadditional components do not prevent the attainment of the object ofthis invention.

The lens resin of this invention can be produced in the followingmanner.

Casting polymerization is usually used to produce lenses. Castingpolymerization is also preferred in the present invention. First of all,the one or more isocyanate compounds (hereinafter called "Component A"for the sake of brevity) and the one or more OH-containing compounds atleast one of which contains one or more sulfur atoms in its molecule(hereinafter called "Component B" for the sake of brevity) are mixed insuch proportions that the NCO/OH ratio falls within the range of0.5-1.5, followed by their stirring. Upon formation of a uniform liquidmixture, it is deaerated. Thereafter, the mixture is poured in a glass-or metal-made mold, in which the reaction of both components is allowedto proceed at a suitable temperature so as to harden the liquid mixture.Component A and Component B may, in many instances, separate into twolayers in an incipient period of their mixing. As their mixing proceeds,the reaction between Component A and Component B is also allowed toproceed further so that the two layers make up a single uniform layer.Even when the deaeration of the uniform liquid mixture has been effectedsufficiently, the reaction may explosively proceed in the mold dependingon the type of Component A or Component B and the reaction may thus beaccompanied by occurrence of bubbles. In order to avoid such aphenomenon, it is necessary to conduct the polymerization reaction whileeffecting sufficient heat removal and precise temperature control.Although the reaction time and reaction temperature vary depending onthe combination of Component A and Component B, the polymerization isgenerally carried out at -20° C.-80° C. for 24 hrs.-72 hrs. The hardnessof the polymer resulting from the reaction reaches the maximum at thetime point where the polymerization reaction has been completed and itdoes not increase beyond that maximum level. The polymerization may bestopped at or before the above-mentioned time point. As a matter offact, the polymerization may be stopped at any time point so long as theresultant resin has sufficient properties as an eyeglass lens of a highrefractive index which the present invention intends to provide. Sincethe starting two-component system is not uniform in many instances inthe above polymerization as mentioned above, it is particularlyimportant to pour and harden the mixture of the two components afterthoroughly stirring and mixing the two components and forming acompletely-uniform single layer prior to their pouring.

In addition to the higher refractive index, the resin of this inventionobtained in the above-described manner has inter alia the followingadvantages over conventionally known lens resins, because it contains Satoms in its backbone.

1. It provides tough plastic lenses.

2. It is colorless and transparent.

3. It has excellent impact resistance.

4. It has good cutting and polishing easiness and is hence superior inmachinability.

5. It has a relatively small shrinkage factor upon its molding andpolymerization.

6. It has a relatively low specific gravity and thus a light weight.

In order to apply some surface modification such as antireflection,higher hardness, improved abrasion resistance, improved chemicalresistance, fog resistance and/or the like, some additional knownphysical and/or chemical treatments may also be applied to a lens whichmakes use of the resin of this invention as its resin component.

Having generally described the invention, a more complete understandingcan be obtained by reference to certain specific Examples andComparative Examples, which are provided herein for purposes ofillustration only and are not intended to be limiting unless otherwisespecified.

EXAMPLE 1

Mixed were 9.4 g (0.050 mole) of m-xylylene diisocyanate as Component Aand 4.3 g (0.050 mole) of di(2-hydroxyethyl) sulfide as Component B. Theresultant mixture was stirred at room temperature or so. Upon completionof a uniform mixture, it was deaerated under ice-cooling. The liquidmixture was then poured into a glass-made lens mold which had beentreated in advance by making it hydrophobic or coating a parting agentthereon so as to facilitate its parting from a resin to be formedtherein. The liquid mixture was allowed to undergo a reaction at 0° C.for 3 hours and then at 20° C. for 20 hours, thereby hardening same.

The resultant lens molding was extremely tough, colorless andtransparent, and had good impact resistance and good cutting andpolishing easiness. Its refractive index (N_(D) ²⁰° C.) was as high as1.59 while its specific gravity was 1.34. Results are shown in Table 1.

EXAMPLES 2-4

In the same manner as in Example 1, Component A and Components Bdescribed in Table 1 were mixed, homogenized, deaerated, poured into aglass-made lens mold and then hardened. Results are shown in Table 1.

Comparative Example 1

Mixed were 9.4 g (0.050 mole) of m-xylylene diisocyanate and 5.3 g(0.050 mole) of diethylene glycol. The resultant mixture was heated withstirring at 40°-50° C., thereby obtaining a homogeneous mixture. It wasthen cooled with water to remove reaction heat.

After deaeration, the liquid mixture was poured in a glass-made lensmold similar to that employed in Example 1 and was then hardened at20°-30° C. for 48 hours. As understood from the results shown in Table1, the resultant lens molding was colorless and transparent and had goodimpact resistance. Its refractive index (N_(D) ²⁰° C.) was 1.56 and itsspecific gravity was as light as 1.18. However, the cutting andpolishing easiness was poor.

COMPARATIVE EXAMPLES 2-3

In the same manner as in Example 1 and Comparative Example 1, ComponentA and Component B were mixed into a uniform mixture. After deaeration,the mixture was poured in a glass-made lens mold, in which it washardened. Results are shown in Table 1.

In Table 1, the following abbreviations will be used. ##STR1##

                                      TABLE 1                                     __________________________________________________________________________    Raw material for polymerization                                               Component A Component B           Property of polymer                         Poly-       S-containing    NCO/OH                                                                              Refractive                                                                            Cutting and                                                                            Specific                                                                            External             isocyanate  polyol          ratio index N .sub.D.sup.20° C.                                                      polishing easiness*                                                                    gravity                                                                             appearance           __________________________________________________________________________    Ex. 1                                                                              m-XDI  HOC.sub.2 H.sub.4 SC.sub.2 H.sub.4 OH                                                         1.0   1.59    O        1.24  colorless,                (0.050 mole)                                                                         (0.050 mole)                                 transparent          Ex. 2                                                                              m-XDI  HOC.sub.2 H.sub.4 SC.sub.2 H.sub.4 SC.sub.2 H.sub.4 OH                                        1.0   1.60    O        1.28  colorless,                (0.050 mole)                                                                         (0.050 mole)                                 transparent          Ex. 3                                                                              TC-m-XDI                                                                             HOC.sub.2 H.sub.4 SC.sub.2 H.sub.4 OH                                                         1.0   1.61    O        1.26  colorless,                (0.050 mole)                                                                         (0.050 mole)                                 transparent          Ex. 4                                                                              HDI    HOC.sub.2 H.sub.4 SC.sub.2 H.sub.4 OH                                                         1.0   1.56    O        1.22  colorless,                (0.050 mole)                                                                         (0.050 mole)                                 transparent          Comp.                                                                              m-XDI  HOC.sub.2 H.sub.4 OC.sub.2 H.sub.4 OH                                                         1.0   1.56    X        1.18  colorless,           Ex. 1                                                                              (0.050 mole)                                                                         (0.050 mole)                                 transparent          Comp. Ex. 2                                                                        m-XDI (0.050 mole)                                                                                   1.0   1.61    Δ  1.52  pale yellow,                                                                  transparent          Comp.                                                                              HDI    HOC.sub.2 H.sub.4 OC.sub.2 H.sub.4 OH                                                         1.0   1.50    X        1.16  colorless,           Ex. 3                                                                              (0.050 mole)                                                                         (0.050 mole)                                 transparent          __________________________________________________________________________     *O: good,                                                                     Δ: relatively poor,                                                     X: poor.                                                                 

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modification can be madethereto without departing from the spirit or scope of the invention asset forth hereon.

What is claimed is:
 1. A sulfur-containing polyurethane base lens resinobtained by reacting one or more isocyanate compounds, which have two ormore NCO groups, with one or more OH-containing compounds selected fromthe group consisting of di(2-hydroxyethyl)sulfide,1,2-bis(2-hydroxyethylmercapto)-ethane, bis(2-hydroxyethyl)disulfide and1,4-dithian-2,5-diol, in such proportions that the ratio of NCO groupsto OH groups ranges from 0.5 to 1.5, at least one of said one or moreOH-containing compounds containing one or more sulfur atoms in themolecule thereof, and the total content of sulfur atoms in allOH-containing compounds being 20 wt. % or higher.
 2. A sulfur-containingpolyurethane base resin as claimed in claim 1, wherein said one or moreOH-containing compounds are di(2-hydroxyethyl)sulfide and/or1,2-bis-(2-hydroxyethylmercapto)ethane.